One of the process steps commonly encountered in the fabrication of integrated circuits and other semiconductor devices is photolithography. Broadly, photolithography involves selectively exposing a specially prepared wafer surface to a source of radiation using a patterned template to create an etched surface layer. Typically, the patterned template is a reticle, which is a very flat glass plate that contains the patterns to be reproduced on the wafer. For example, the wafer surface may be prepared by first depositing silicon nitride on it followed by a coating of a light-sensitive liquid polymer or photoresist. Next, ultraviolet (UV) light is shone through or reflected off a surface of a mask or reticle to project the desired pattern onto the photoresist-covered wafer. The portion of the photoresist exposed to the light is chemically modified and remains unaffected when the wafer is subsequently subjected to a chemical media that removes the unexposed photoresist leaving the modified photoresist on the wafer in the exact shape of the pattern on the mask. The wafer is then subjected to an etch process that removes the exposed portion of the nitride layer leaving a nitride pattern on the wafer in the exact design of the mask. This etched layer, singly or in combination with other similarly created layers, represent the devices and interconnects between devices characterizing the “circuitry” of a particular integrated circuit or semiconductor chip.
With extreme ultraviolet (EUV) photolithography, reflection from the patterned surface is used as opposed to transmission through the reticle characteristic of deep ultraviolet light photolithography. Consequently, the reflective photomask (reticle) employed in EUV photolithography is susceptible to contamination and damage to a far greater degree than reticles used in conventional photolithography. Particulate contamination of the surface of the reticle can compromise the reticle to a degree sufficient to seriously affect any end product obtained from the use of such a reticle during processing. Particles can be generated within the controlled environment containing the reticle during processing, transport and shipping. Sliding friction between the reticle and the container and between the components of the container are also sources of contaminating particulates. Also, it is now known that gases and minute quantities of moisture can escape from the polymer materials used in reticle containers, which can cause haze and crystal growth on reticles damaging the same.